It is known to provide an evaporative fuel handling apparatus having a purge system. The purge system purges evaporative fuel produced in a fuel tank into an air intake system of an engine. Technology has been proposed for performing forcible purge of evaporative fuel into an air intake system by producing a pressure difference with a pump between the inside and outside of the purge system (see, e.g., U.S. Pat. No. 6,695,895, JP-2002-332921A). Technology has also been proposed for checking for leaks in the purge system by producing a pressure difference with a pump between the inside and outside of the purge system (see, e.g., U.S. Pat. No. 7,004,013, JP-2004-28060A).
The size and weight of the evaporative fuel handling apparatus could be reduced if the same components operate for both forcibly purging and checking for leaks. For instance, the size and weight could be reduced by using a pump common to both purging and leak checking operations. However, the requirements for pump for performing forcible purge are substantially different than those of a pump for leak checking. As such, incorporation of a common pump can be difficult.
More specifically, the pump for performing forcible purge (i.e., the purge pump) provides a relatively large flow rate for purge and sets a produced pressure at a specified value lower than a threshold value at which resistance to pressure exists. Hence, as shown by the solid line of FIG. 7, a characteristic curve relating pressure (P) and flow rate (Q) for the purge pump has a relatively large slope. Like the purge pump, the pump for leak checking sets a produced pressure at a specified value lower than a threshold value at which resistance to pressure exists; however, the pump for leak checking increases the change in produced pressure with respect to a change in flow rate. Hence, as shown by the broken line of FIG. 7, the slope of the characteristic curve relating pressure (P) and flow rate (Q) is lower. Thus, for example, if a pump set for performing forcible purge is used for leak checking, the slope of the P-Q characteristic curve is likely to be too large. Hence, a change in pressure with respect to a change in flow rate becomes too small, which causes reduced accuracy when leak checking.